The overall goal of this project is to determine whether the elevated rate of breast cancer in Massachusetts can be considered to vary from place to place at random throughout the state, or whether the rate is excessive in specific geographic areas. And, if there are areas of excess, whether that excess is stable or temporary over the study years, whether excesses are consistent across all diagnostic stages, or whether excesses might be due, for example, to excesses in early or late stage diagnoses, and whether they can be attributed to covariates such as age, fertility, race/ethnicity, education, or economic conditions. The specific aims are: (1) to test for the presence of statistically significant spatial clusters of excess breast cancer and to do so at the level of the census tract, ZIP code, and town; (2) to test for statistically significant spatial clusters of excess breast cancers by diagnostic stage; (3) if statistically significant clusters are found, to test whether the excesses at those locations have been consistent and continuous over the study years, or are temporary or sporadic; and (4) to test whether clusters remain after adjustment for selected social, economic, and demographic measures from the US census, such as race/ethnicity, education, fertility, and economic factors. The incidence file contains information of 57,560 cases diagnosed between 1982 and 1994, and includes the year, month, and day of diagnosis, the summary stage based on SEER's staging convention (in situ, local, regional, distant, and unknown), race, city/town, ZIPcode, census tract, and latitude/longitude of patient's address. Analyses will be conducted with data aggregated to census tracts, ZIP codes, towns, along with disaggregated analyses at the level of the individual case using the Spatial Scan statistic to determine whether areas of excess can be "explained" by chance or other covariate information, whether areas of excess are stable over time, or whether they vary by diagnostic stage.